On April 16, the Department of Environmental Protection announced the beginning of its 2021 Black Fly Suppression Program. The program involves aerial and backpack spraying on roughly 1,700 stream miles in 35 counties of the Commonwealth.

“Black flies are a seasonal pest that can cause emotional stress to people seeking outdoor recreation,” said DEP Secretary Patrick McDonnell. “This initiative reduces the black fly population so that Pennsylvanians and visitors can fully enjoy our natural resources.”

This year, 48 rivers and streams spanning more than 1,700 miles will be monitored and treated as needed. Spraying activities will be performed both by helicopter and ground crews.

The frequency will depend on weather and biological conditions. Treatments cannot occur during periods of heavy rain or when water levels are high as these conditions lower the effectiveness of the treatment and significantly increase the cost of the control operations.

DEP uses Bti, a naturally occurring bacterium, to treat the larval stage of four specific human pest black fly species. This bacterium degrades quickly in the environment and does not harm the aquatic ecosystem, birds, or other insects.

Prior to any spraying activity, DEP notifies county and local emergency management officials. Helicopters can be seen flying over waterways and ground crews using backpack sprayers off bridges and wading in streams conducting control operations on behalf of DEP’s Black Fly Suppression Program.

Anyone concerned at the sight of a helicopter or ground personnel is encouraged to call their county emergency management office to verify that a black fly treatment is taking place in their area on that day.

For more information, visit DEP’s Black Fly Program webpage.

[Posted: April 16, 2021]

4/19/2021